Rare-earth containing oxide nanocomposites are prepared of porous GaP and GaAs templates in a controlled fashion. The initial porous GaP and GaAs networks are replaced by GaPO4 and Ga2O3 structures, respectively, during annealing at emperatures from 500 to 900 o C. The impregnation of Eu and Er lanthanides from EuCl3:C2H5OH and ErCl3:C2H5OH solutions results in the formation of lanthanide containing oxide microcrystals finely dispersed into the native oxide matrix. These oxide phases are found to be EuPO4 and ErPO4 in composites obtained on GaP templates, and EuAsO4 and ErAsO4 in composites prepared on GaAs templates. 4f-4f intrashell transitions in Eu3 and Er3 ions assure strong red and green emission from these nanophases.